A known device for testing a brake fluid and detecting its boiling point comprises a heating cup into which some of the fluid is injected with the aid of a syringe. After being closed against the atmosphere, the cup is heated until evolving gas bubbles begin to pass through a U-shaped tube into a receptacle therefor. The temperature at which this occurs is noted as the boiling point, whereupon the liquid in the cup is returned to the brake system of the vehicle by means of the same syringe; both the cup and the syringe are then carefully cleansed preparatorily to a new test. Such a device is relatively expensive and cumbersome to handle, being thus not very well suited for use in a repair shop for automotive vehicles.
In my above-identified copending application and patent I have disclosed a method of boiling-point determination according to which a quantity of the liquid to be tested is confined in a narrow boiling chamber that is closed at the top and is in communication at its bottom with a larger body of the same liquid. During gradual heating of the liquid so confined, the temperature in the space is continuously measured. When that liquid begins to boil, the rate of temperature rise undergoes a significant change; thus, if the temperature is measured near the top of a narrow test space from which the liquid is quickly displaced by evolving vapors, the heat generated in the vicinity of the sensor used for the temperature measurement is less rapidly conducted to the larger body of liquid so that the rate of temperature rise undergoes a steep increase. Such a rate change is taken as an indication that the boiling point has been reached.
While the system described in my prior U.S. Pat. No. 4,408,902 operates satisfactorily, it requires the use of two separate instruments to measure the actual temperature as well as the temperature rise. Another inconvenience is the need for sealing the boiling chamber against the atmosphere during a test.